how to use preconditioner Kerker for convergence?

[Anders Blom]

No, not really. There are no universal answers, one would need to look at the particular simulation. It may be the central region is too short, or the electrode is too short.

[kaypu]

thank you professor Anders, this is my system, i think it is enough for the center scattering area and electrode, but it still hard to converge in higher bias(more than 1.1V), why?

the band gap of the electrode is about 1eV, so i should decrease the electrode temperature, because Fermi broadening is useless for the electron occupied in the band gap. Maybe this will lead to misconvergence. am i right?

[Anders Blom]

The main problem might be that there isn't really any scattering in this system. It's a perfectly periodic structure, so it's pointless to run a huge transport calculation for it. The transport properties are formally determined purely by the zero-bias transmission spectrum - and in fact you could even compute the transmission spectrum from the electrode alone.

The point is that there is not natural place of resistance in the system, so there is no place for the voltage to drop at finite bias, when you run it as a device calculation. Thus it's very natural that it's hard to converge at high bias, but as mentioned above, even at small finite bias, you are really making a rather pointless simulation.

Apart from that, this also highlights the importance of providing all relevant information from the beginning. Both of us could have saved lots of time if the system had been included in the first post on this topic.

[kaypu]

i'm so sorry about that professor Anders

but i have read some of papers studying transport property of graphenenanoribbon, such as APPLIED PHYSICS LETTERS 94, 173110,  JOURNAL OF APPLIED PHYSICS 110, 013718,  J. Phys. Chem. C 2012, 116, 5915−5919,

both of them studied transport property of nanoribbon as shown in fig1 and fig2 (J. Phys. Chem. C 2012, 116, 5915−5919), they report perfect  transport property of ZGNR junctions and i-v curse shown in fig2

i just want to simulate the effect of different edge to the transport property under different bias, is that pointless?

Regards

[Anders Blom]

It would argue that the GE0 result of that article is somewhat artificial, but it's not really the topic of the paper. The simulations done for various protrusions on the edge are perfectly valid. The point is that in these cases the central region is different from the electrodes.

If you want to know the ballistic transport properties of a perfect graphyne ribbon (with different edges or whatever), I would recommend to just compute the transmission spectrum for the electrodes at zero bias, a very quick calculation. Then you can get a linear response I-V curve (you can borrow the Analyzer from here), it's the best you can do for a perfectly periodic system anyway.

[kaypu]

thank you professor Anders

the band gap of graphyne nanoribbon is 1eV, during 0-1V, the current is almost 0, not a liner i-v, see fig, the TE changes a lot with the increasing of the bias, i think the method will be wrong during the 1.1-2V or higher.

[Anders Blom]

Why wrong?

[kaypu]

TE is different in different bias, and it changes a lot, it may be wrong to obtain i-v using zero-bias TE. under low bias 0-0.9V, the current is zero, the method is right, as shown in fig1, integration is always 0.
but higher than 0.9V, the integration will increase a lot.

fig2 shows TE in 0.9, the integration is 0. 

it is inconsistent

[Anders Blom]

You would be correct if there was scattering in the central region, but not for the perfect ribbon. The fact that you get T(E) to be bias-dependent in your device calculation for the perfectly periodic structure is essentially an artifact of the model.

[kaypu]

thank you professor Anders, i will change the scattering region.

so sorry to waste your time

regards